An example of the LC cross-coupled oscillator that includes a resonator configured by an inductor and a capacitor is disclosed in JP-A-2004-260301. Further, in D. B. Leeson, “A Simple Model of Feedback Oscillator Noise Spectrum”, Proc. IEEE, vol. 54, pp. no. 2, 329-330, February 1966, a phase noise power of an oscillator in a small signal model is disclosed. Further, in A. Hajimiri and T. H. Lee, “A general theory of phase noise in electrical oscillators” IEEE J. Solid-State Circuits, vol. 33, pp. 179-194, February 1998, a phase noise power in the large signal model is disclosed. Furthermore, an example of an oscillator in which the tail current source is removed from an LC cross-coupled oscillator and a common ground point of a differential amplifier is directly connected with a circuit ground is disclosed in Ping-Chen Huang, “A 131 GHz Push-push VCO in 90-nm CMOS Technology”, IEEE RFIC, 2005. An example of an LC cross-coupled oscillator that does not have a tail current source is described in T. Song, “A 5 GHz Transformer-Coupled CMOS VCO Using Bias-Level Shifting Technique”, IEEE RFIC 2004.